ACR 23 Finals Prep
The heat transfer rate for natural-draft evaporators is approximately _____.
1 BTU/HR x ft squared x degrees Fahrenheit
Air-cooled condensers in commercial systems generally have a temperature difference of _____.
10-30 degrees Fahrenheit
Liquid receivers should be sized _____ larger than the total liquid volume in a system.
15%
For most refrigerant lines, the maximum allowable pressure drop is equal to a saturation temperature drop of _____.
2 degrees Fahrenheit
Total head load represents the amount of heat that a commercial refrigeration system must remove in a(n) _____ period.
24-hour
The heat transfer rate for forced-draft evaporators is approximately _____.
3 BTU/HR x ft squared x degrees Fahrenheit
The ARI standard recommends that chiller evaporators operate at a chilled water temperature of ______.
44 degrees Fahrenheit
A chiller with a centrifugal compressor has an oil pump that is driver by_____.
A separate motor
The refrigerant in the secondary loop of a secondary loop refrigeration system _____.
Absorbs heat but does not evaporate
The main method of capacity control used by a centrifugal compressor is done by _____.
Adjusting the guide vanes
The main method of capacity control used by a screw compressor is done by _____.
Adjusting the slide valve
A secondary loop system uses a(n) _____ to trap air circulating with the secondary refrigerant.
Air separator
A hot-gas bypass valve _____. A) warms the cool suction gas, raising the pressure in the suction line. B) is connected by its inlet to the discharge line C) opens if the low-side pressure becomes excessively low
All of the above
A vortex tube _____. A) Simple device that provides cold air by separating it from hot air. B) has no moving parts C) does not use refrigerant.
All of the above
After an outdoor compressor has cycled off and when ambient temperature is very low, _____. A) refrigerant inside the compressor could condensed into liquid B) there is a danger of slugging and damage may lead to failure C) a crankcase heater may be used to prevent refrigerant from condensing
All of the above
For a reciprocating compressor, the theoretical compressor volume is determined by the ______. A) number of cylinders B) bore C) stroke
All of the above
In a system in which hot gas from the compressor is bypassed directly to the evaporator inlet, _____. A) the hot gas increases the load B) the system can continue running while maintaining the desired temperature C) temperature and humidity can be controlled more precisely
All of the above
In some larger-capacity trucks, an externally mounted generator provides the power for the ______. A) Compressor B) Condenser fans C) Evaporator fans
All of the above
The required minimum velocity for a refrigerant line depends on the _____. A) temperature of the refrigerant B) type of refrigerant C) size of the line
All of the above
When compressed air is released in a vortex tube, _____. A) the jet acts as an internal Venturi B) a large volume of hot air comes out one end of the tube C) smaller volume of cold air comes out the other end.
All of the above
Which of the following statements about cooling towers is true? A) Housing or shed into which air is drawn. B) Used when tap water cannot be used and then dumped to cool a condenser. C) Makeup water is added to replace water lost by evaporation.
All of the above
If the heat load is light, _____.
An oversized system will tend to short cycle.
Which of the following statements regarding pressure drop is false? A) If the lines are too small, they create excessive pressure drop. B) Pressure drop is affected by line diameter C) Each bend in the line causes additional pressure drop. D) As the length of the line increases, the pressure drop decreases.
As the length of the line increases, the pressure drop decreases.
A secondary loop refrigeration system controls flow using a _____.
Balancing valve
A water valve's main body is most often installed in a system _____.
Between the water supply and condenser
The process in which some water is intentionally drained for the purpose of reducing certain mineral concentrations in a cooling tower's water is referred to as _____.
Blowdown
A valve that is used to protect the compressor from higher than normal pressure vapor from the suction line is a(n) _____.
CPR
A valve that protects the compressor from higher than normal pressure vapor from the suction line.
CPR
A valve that protects the compressor from higher than normal pressure vapor from the suction line is a(n) ______.
CPR (crankcase pressure regulator)
The oil pump used with a chiller's centrifugal compressor _____.
Can provide lubrication even before the compressor begins turning.
A multistage system that consists of two or more separate refrigeration systems that work together to multiply cooling effect is a _____.
Cascade refrigeration system
To prevent backward flow of refrigerant when the system is shut down, a scroll compressor uses a _____.
Check valve
Secondary loop systems use _____ to move the secondary refrigerant.
Circulating pump
A compound refrigeration system can produce such low temperatures because it uses two _____.
Compressor connected in series
As the flow of secondary refrigerant the temperature of the conditioned space _____.
Decreases
When a chiller's compressor uses cylinder unloading, compressor power consumption _____.
Decreases
The valve used to allow hot-gas refrigerant from the discharge line to enter the evaporator and flow into the low side of the system is a hot-gas _____ valve.
Defrost
A service valve located between a compressor and condenser.
Discharge service valve
A valve that is used to restrict the flow of refrigerant coming out of the evaporator is a(n) _____.
EPR
A valve that restricts the flow of refrigerant coming out of the evaporator.
EPR
A valve that restricts the flow of refrigerant coming out of one evaporator in a multiple evaporator system is a(n) ______.
EPR (evaporator pressure regulator)
An anti-icing control monitors the temperature of the _____.
Evaporator
(T/F) A commercial refrigeration system's liquid line must always be insulated.
False
(T/F) A double suction line should consist of two lines of equal size.
False
(T/F) A thermostatic water valve uses a sensing bulb to monitor subcooling.
False
(T/F) An EPR is used to maintain evaporator pressure below suction line pressure.
False
(T/F) Chiller compressors are designed so that all of the cylinders are unloaded at the same time.
False
(T/F) Dry ice is is carbon monoxide (CO) frozen solid.
False
(T/F) In a refrigerant jet stream, the temperature of the refrigerant leaving the evaporator is much higher than the temperature of the refrigerant leaving the heat exchanger.
False
(T/F) Of all types of compressors used with chillers, reciprocating compressors produce the lowest levels of noise and vibration.
False
(T/F) Split systems cannot be custom designed for specific applications.
False
(T/F) The compressor motors used on compound systems do not need to be able to start under load.
False
(T/F) The thicker the evaporator's material, the greater the heat transfer.
False
(T/F) Thermoelectric couples are designed to produce an electric current when heat is applied.
False
(T/F) Thermoelectric couples are thermocouples are interchangeable.
False
To effectively remove noncondensables from a well maintained chiller, a purge unit will run _____.
For short periods of time
A water-filled container on top of a cooling tower that has precision holes through which accumulated water flows onto wet decks is a(n) _____ basin.
Gravity flow
What is used in a trailer refrigeration system to allow heated vapor refrigerant to enter the evaporator?
Hot gas solenoid valve
A valve that allows regulated amounts of hot refrigerant vapor to enter the low side of the system.
Hot-gas bypass valve
A valve that directs hot-gas refrigerant from the discharge line to enter the evaporator to melt accumulated ice.
Hot-gas defrost valve
A valve used to reduce the temperature of the hot gas by allowing liquid refrigerant from the liquid line to mix with and cool the bypassed hot refrigerant vapor is a _____
Liquid injection valve.
A device used to connect or isolate the main liquid line from the different evaporators.
Liquid line manifold
When a high-side service valve is located between a condenser and a refrigerant metering device, it may be referred to as a _____.
Liquid line service valve
A valve used to isolate the liquid receiver from the test of the system.
Liquid receiver service valve
When extremely low temperatures must be produced, it is best to use a _____.
Multistage system
A cooling tower that relies on wind and natural convection to blow through the tower to aid in evaporation is a(n) _____ cooling tower.
Natural-Draft
A commercial refrigeration system that is designed, built, and shipped by the manufacturer is referred to as a _____ system.
Packaged
Refrigeration units designed, built, and shipped by the manufacturer are referred to as _____ systems
Packaged
A water valve that regulates water flow based on the valve's bellow's reaction to high side pressure is a _____ water valve.
Pressure
A collection of components used in a cooling tower that pumps water through pipes and out of spray heads along the top of the tower is called a(n) _____ system.
Pressured water
A crankcase heater is used to _____.
Prevent refrigerant from condensing into liquid
What is used in a trailer refrigeration system to allow liquid refrigerant into the suction line to cool the compressor motor?
Quench valve
Which of the following statements about RTUs is false? A) Parts are purchased individually and assembled on site. B) Openings on the roof may develop leaks. C) They do not take up interior space. D) They should be weatherproofed.
RTU parts are purchased individually and assembled on site.
A centrifugal compressor chiller's economize does what?
Reduces refrigerant pressure to produce flash gas for liquid line subcooling.
To prevent water from leaking through the opening, a _____ must be installed between the base rail of a RTU and the top edge of the roof curb.
Resilient gasket
A fluid that is circulated to absorb heat from a conditioned space is a(n) _____ refrigerant.
Secondary
While purge units do help keep chillers running well, they will release _____ on occasion.
Small amounts of refrigerant to the atmosphere
What is used in a trailer refrigeration system to remove additional heat from a refrigerant leaving the liquid receiver?
Subcooler
Vibration absorbers are installed in a truck or trailer refrigeration system on _____
Suction and discharge lines
A device used to connect or isolate the different evaporators from the main suction line.
Suction line manifold
A low-side service valve located along the suction line.
Suction line service valve
A low-side service valve connected to the inlet or the low side of the compressor.
Suction service valve
A service valve connected to the inlet or the low side of the compressor is a _____.
Suction service valve
Once the relative humidity of the conditioned space is selected based on the product being refrigerated, the _____ can be determined.
Temperature difference
Which of the following statesmen's about a steam jet system is false? A) the bottom part is filled with water vapor, and the rest is filled with water. B) high pressure steam is used to induce low pressure in the evaporator. C) steam jet systems are typically used for air conditioning. D) As water in the evap begins to evaporate, it absorbs heat from the remaining water.
The bottom part is filled with water vapor and the rest is filled with water
The saturated suction line temperature can be calculated by subtracting the temperature difference from the design temperature of ____.
The conditioned space
In a Sterling cycle, _____. A) the space between the pistons is usually charged with helium B) The heat exchangers are insulated C) the regenerator is filled with a nonporous material
The space between the pistons is usually charged with helium
Cylinder unloading is commonly accomplished by holding _____.
The suction valve open
The process of transferring heat energy from one place to another using the movement of electrons is _____ refrigeration.
Thermoelectric
A water valve that regulates water flow to a water-cooled condenser based on the temperature of condenser exhaust water is a(n) ______ water valve.
Thermostatic
Which of the following systems regarding cascade systems is true? A) They operate at very low temperatures so the refrigerant must be very dry. B) They are more compact than a conventional refrigeration system. C) They are mostly in small domestic appliances
They operate at very low temperatures so the refrigerant must be very dry
The equivalent length for each fitting and valve in a line is added to the length of the line itself to find the line's ____.
Total equivalent length
(T/F) As a chiller circulates water through a building, the water absorbs and removes heat from the conditioned spaces.
True
(T/F) Bypassed hot gas can help prevent compressor damage and short cycling of the system.
True
(T/F) Cylinders containing liquid nitrogen should not be rolled.
True
(T/F) Low-temperature lines require higher velocities than high-temperature lines because oil flows less easily at lower temperatures.
True
(T/F) Suction line problems can be avoided in a modulating refrigeration system by using a double suction line with one small line and one larger line.
True
(T/F) The type of compressor used in a chiller system may depend on the number of tons of air conditioning needed.
True
(T/F) The volume displaced by the piston on each stroke is the volume of the refrigerant vapor moved through the compressor.
True
A flexible section of piping that isolated the vibrations produced by the compressor is called a _____.
Vibration absorber